<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN""http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
<title>js</title>
<link rel="stylesheet" type="text/css" href="">
</head>
<style type="text/css">
html,body{height:100%;overflow:hidden;}
body,div,h2{margin:0;padding:0;}
body{font:12px/1.5 Tahoma;}
center{padding-top:10px;}
button{cursor:pointer;margin: auto;}
#overlay{position:absolute;top:0;left:0;width:100%;height:100%;background:#000;opacity:0.5;filter:alpha(opacity=50);display:none;}
#win{position:absolute;top:50%;left:50%;width:400px;height:200px;background:#fff;border:4px solid #f90;margin:-102px 0 0 -202px;display:none;}
h2{font-size:12px;text-align:right;background:#FC0;border-bottom:3px solid #f90;padding:5px;}
h2 span{color:#f90;cursor:pointer;background:#fff;border:1px solid #f90;padding:0 2px;}
</style>
<body>
  <center>
  	<button>弹出层</button>
  </center>
  <div id="overlay" >	
  </div>
  <div id="win" >
  	<h2>
  		<span id="close">x</span>
  	</h2>
  </div>
 <script type="text/javascript">
 	var aBtn = document.getElementsByTagName('button')[0];
 	var oDiv1 = document.getElementById('overlay');
 	var oDiv2 = document.getElementById('win');
 	var oSpan = oDiv2.getElementsByTagName('span')[0];
 	aBtn.onclick = function(){
 		oDiv1.style.display = 'block';
 		oDiv2.style.display = 'block';
 	}
 	oSpan.onclick = function(){
 		oDiv1.style.display = 'none';
 		oDiv2.style.display = 'none';
 	}
 </script>
</body>
</html>